1. Field of the Invention
The present invention relates to a solid-state image pickup apparatus and a production method thereof, more specifically, to a solid-state image pickup apparatus having a structure in which a waveguide is formed above a charge generation portion and a hollow portion (void portion) is provided around the waveguide, and a production method thereof.
2. Description of the Related Art
When incident light obliquely enters a charge generation portion (light-receiving portion) of a unit pixel of a solid-state image pickup apparatus, instead of entering a charge generation portion of a unit pixel that the light is supposed to enter, the light may enter a charge generation portion of an adjacent unit pixel different from that unit pixel due to stray light to be subjected to a photoelectric conversion. In this case, since the incident light cannot be used effectively in the original unit pixel, a sensitivity is lowered and image pickup characteristics between the adjacent pixels (inter-pixel crosstalk) are deteriorated.
As a countermeasure, there is proposed a solid-state image pickup apparatus that includes a hollow portion (air gap, gas layer) for collecting incident light at a charge generation portion to effectively use the incident light (see, for example, Japanese Patent Application Laid-open No. 2008-10544 (hereinafter, referred to as Patent Document 1) and Japanese Patent Application Laid-open No. 2005-175072 (hereinafter, referred to as Patent Document 2)). A leitmotif is a technique of guiding, by forming a hollow portion in an interlayer film or between a waveguide and the interlayer film and totally reflecting light using a refractive index difference between the interlayer film and the hollow portion, oblique incident light toward the charge generation portion to thus lower a possibility of the oblique incident light entering an adjacent pixel.
FIGS. 6 and 6A are diagrams for explaining a structure described in Patent Document 1. When producing a solid-state image pickup apparatus 1X, a charge generation portion 902 is first formed on a surface layer of a substrate 900 formed of a semiconductor material such as single-crystal silicon. Oxide films whose compositions are changed by differentiating etching rates so that the etching rates increase toward the upper layer are laminated on the substrate 900, that is, interlayer films having different etching rates are laminated (oxide-film laminating process). As an example, a BPTEOS film 911 is deposited as a lower layer on the substrate 900 side and a P—SiO film 912 formed by a plasma CVD method is deposited on the BPTEOS film 911 as an oxide film. Then, trenches are formed by dry etching processing (trench-forming process) (FIG. 6(1)). Subsequently, using a difference between the etching rates of the laminated interlayer films (BPTEOS film 911 and P—SiO film 912), a trench width of only the BPTEOS film 911 as the lower layer is intentionally widened by wet etching (selective trench-width widening process: FIG. 6(2)).
Next, a hollow portion 950 is formed by overhanging filling by CVD with poor coverage (filling process: FIG. 6(3)). However, since a streak (line) is formed in the hollow portion 950 with only the overhanging filling, etch back and deposition are repeated by HDP (High Density Plasma)-CVD to thus close up the streak.
Patent Document 1 also discloses an example of forming a hollow portion 950 to be higher than an upper-layer wiring as in a solid-state image pickup apparatus 1Y shown in FIG. 6A.
In Patent Document 2, after forming a dummy film for forming a hollow portion after processing a waveguide and filling an organic dielectric film after removing the unnecessary dummy film at the bottom of the waveguide, a part of the interlayer film at an upper layer of the dummy film at an opening portion of the waveguide is etched selectively to expose the dummy film. By selectively etching only the dummy film using gas that has F (fluorine) or Cl (chlorine) as a main component of etching, such as CF4 and CCl4, for example, a hollow portion is formed. Further, by forming, after forming the hollow portion by selectively etching the dummy film, a thin liner film at a side wall portion by a P-CVD (plasma CVD) method or a UV-CVD (ultraviolet light CVD) method at low temperature while using a difference in deposition rates between the waveguide opening portion and the side wall portion, an opening of the waveguide opening portion is closed up.